Temperature gauge does not work on my 1970 340 Duster ?

DaveM said

Here is what I have done so far during troubleshooting this prob.

1) grounded the sending unit wire, gauge moves up to 'H' (means the gauge should be good)
2) replaced sending unit with a new unit, gauge does not move??
3) connected my orig sending unit to the sending unit wire and grounded the threads of the unit. Then heated up the sending unit, gauge registered/moved accordingly towards 'H' !

Why doesn't the gauge work with the original sending unit installed in the manifold??
Could the gauge still be bad even though it moves when grounding the sending unit?
Not sure if it is related but my gas gauge reads empty. I will try grounding its sending unit wire as well....any help would be appreciated.

Click to expand...

Let's go back to square one..................see the photo?


Those resistance values in yellow, someone edited that to reflect the factory tester values. If you can heat your old sender and get it close to one of those values, then stick it in the circuit from block to sender wire, and if the gauge reads somewhat close (of course it will change--------the sender is cooling down!!!

THEN THE ENTIRE GAUGE CIRCUIT is likely OK, or at least "OK enough" that you can move forward

I tried to tell you earlier..........with the engine "somewhat warm" take your meter and measure the resistance from the sender stud to the sender brass. That should give you some idea based on temperature (see the photo) of whether the sender is good

Measure resistance from the sender brass to some known ground........LOL....LIKE THE BATTERY NEGATIVE POST. It should be close to zero

Try subbing in the old sender and see if these values change.

ANOTHER THING you can try is to connect the temp sender (jumper clip wire) to the oil sender wire. THIS WILL TURN THE OIL PRESSURE GAUGE into a TEMPERATURE gauge. You can also do the opposite............jumper the temp sender wire to the oil sender and that should cause the temp gauge to read OIL PRESSURE